This invention relates to composite structures such as for example composite firearm barrels.
It is known to construct strong, light structures using composite materials such as for example light weight but stiff barrels for firearms. In one known type of composite structural member, a central member is reinforced by an outer composite jacket comprised of strands or tows embedded in a resin. In some such structures, at least some of the tows are helically wound about the central member. One type of composite gun barrel includes an inner tubular member of a hard material such as steel forming and enclosing the bore of the barrel and an outer jacket of a composite material that includes tows helically wound about the inner tubular member.
In some prior art composite gun barrels, the jacket has several layers with the tows in each layer having a different winding angle and/or some other different property or properties intended to enhance a particular characteristic such as bursting strength, torsional stiffness or bending stiffness. One such prior art patent is U.S. Pat. No. 4,685,236 to Sam May. In this type of prior art gun barrel, the composite jacket and the liner are substantially uniform along their length or have only gradual changes in diameter of the composite jacket.
This prior art type of gun barrel has several disadvantages such as for example: (1) its accuracy is reduced by excessive variations in the angle the muzzle is pointing at the moment of exit of the projectile caused by high amplitude vibrations at the muzzle end of the barrel; and (2) some embodiments are excessively susceptible to overheating during use. In the prior art, the muzzle angle is stabilized by trimming the length of the barrel to a point where the muzzle is at a node of low amplitude vibrations. However, this technique is time consuming and difficult.
Some prior art structural members such as the shafts of golf clubs are formed of composite materials with the fibers wound in helixes having a winding angle that changes along the shaft and with multiple winding angles on different layers to control the kick point along the shaft and suppress reflected vibration from the grip of the club. Two such patents are U.S. Pat. No. 4,319,750 to Roy and U.S. Pat. No. 4,157,181 to Cecka. These patents are not adapted to use for barrels or for devices in which there is a gas propelled projectile to be expelled from a muzzel or which require the dissipation of heat.
The prior art composite barrels commonly include a liner as the tubular member forming the bore of the firearm with its internal walls. The liner is usually too thin to be used alone as a barrel in the firearm without reinforcement. This type of composite barrel has the disadvantage of having poorer burst strength, poorer thermal conductivity along and through the barrel and wider vibrational swings of its muzzle end.
To reduce vibration, one type of prior art composite barrel couples the composite to the steel lining more tightly by compressing the composite against the steel liner to cause the vibrations to be absorbed in the matrix. Some also align the tows with the barrel so that longitudinal vibrations compress the tows in the direction of low resistance and extend the tows by releasing the compression along their length so the vibrations are absorbed and attenuated in the resin matrix. However, these measures under some circumstances do not sufficiently reduce vibrations. The use of tows aligned with the longitudinal axis of the bore also has the disadvantage of reducing the resistance to radial pressure as compared to the composites having tows cylindrically or helically wound or formed in a plane perpendicular to the longitudinal axis of the barrel thus requiring a thicker inner tube or more reinforcement. Prior art firearms with composite barrels have generally not been gas operated. This is because the composite jacket would be exposed to hot gas and heat to the extent that the composite would be degenerated, in fast firing weapons. Moreover, in some such structures, the thermal coefficients of expansion are incompatible resulting in structural weaknesses and faults during temperature changes.
Some prior art composite structures include thermally conductive primary metallic base materials such as titanium metallic materials. An example of such a composite material is disclosed in U.S. Pat. No. 6,284,389 to Jones et al., granted Sep. 4, 2001. However, such composite materials have not been used in conjunction with firearm barrels although the need for controlling the heating of firearm barrels has long been known and thermally conductive materials have long been known. One difficulty in adding conductive materials to composite firearm barrels is that some such materials increase the viscosity or change other characteristics of the composite in a manner that makes winding of the tows difficult or alters the ability of the composite jacket to maintain its integrity under high temperatures. For example, some high thermal conductivity tows have a coefficient of thermal expansion that is negative and so large as to cause separation of the jacket and the liner if used.